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Vlasák Pavel - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of settling slurry flow in inclined Pipe sections
2018Co-Authors: Vlasák PavelAbstract:Narrow particle size distribution glass beads-water slurry flow in the Pipe sections of different inclination were investigated on an experimental Pipe loop of inner diameter D = 100 mm. The study refers to the effect of Pipe inclination and slurry velicity on local concentration distribution, pressure drop-velocity relationship, and deposition limit. The study revealed that the glass beads-water mixtures in the inclined Pipe sections were significantly stratified: the solid particles moved principally close to the Pipe Invert, and for flow velocities close to the deposition limit sliding bed or stationary deposit is created even in inclined Pipe sections
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Flow behaviour and structure of heterogeneous particles-water mixture in horizontal and inclined Pipes
EDP Sciences, 2018Co-Authors: Vlasák Pavel, Chára Zdeněk, Konfršt JiříAbstract:The effect of slurry velocity and mean concentration of heterogeneous particle-water mixture on flow behaviour and structure in the turbulent regime was studied in horizontal and inclined Pipe sections of inner diameter D = 100 mm. The stratified flow pattern of heterogeneous particle-water mixture in the inclined Pipe sections was revealed. The particles moved mostly near to the Pipe Invert. Concentration distribution in ascending and descending vertical Pipe sections confirmed the effect of fall velocity on particle-carrier liquid slip velocity and increase of in situ concentration in the ascending Pipe section. Slip velocity in two-phase flow, which is defined as the velocity difference between the solid and liquid phase, is one of mechanism of particle movement in two-phase flow. Due to the slip velocity, there is difference between transport and in situ concentrations, and the slip velocity can be determined from comparison of the in situ and transport concentration. For heterogeneous particle-water mixture flow the slip velocity depends on the flow structure
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Flow of heterogeneous slurry in horizontal and inclined Pipes
2017Co-Authors: Vlasák PavelAbstract:Narrow particle size distribution heterogeneous slurries were investigated on an experimental Pipe loop with the horizontal and inclined Pipe sections of inner diameter 100 mm. The investigation was focused on the effect of the Pipe inclination, average slurry velocity and overall concentration and on the local concentration distribution, pressure drop, deposition limit and carrier liquid-particle slip velocity. The local concentration distribution was studied with the application of a gamma-ray densitometer. Mixture flow-behaviour and particles motion were investigated in a Pipe viewing section. The study revealed that the heterogeneous slurries in the horizontal and inclined Pipe sections were significantly stratified, the solid particles moved principally close to the Pipe Invert, and particle saltation becomes the dominant mode of particle conveying for higher and moderate flow velocities. Carrier liquid-particle slip velocity depends not only on the mixture velocity, but also on particle position in the Pipe cross-section. The effect of Pipe inclination on the frictional pressure drop in inclined Pipe sections depends on mixture velocity, in ascending Pipe section decreases with increasing mixture velocity and in descending Pipe section the frictional pressure drop gradually decreased with increasing Pipe inclination
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Flow behaviour and local concentration of coarse particles-water mixture in inclined Pipes
Sciendo, 2017Co-Authors: Vlasák Pavel, Chara Zdenek, Konfrst JiriAbstract:Narrow particle size distribution basalt pebbles of mean particle size 11.5 mm conveyed by water in the Pipe sections of different inclination were investigated on an experimental Pipe loop, consisting of smooth stainless steel Pipes of inner diameter D = 100 mm. Mixture flow-behaviour and particles motion along the Pipe Invert were studied in a Pipe viewing section, the concentration distribution in Pipe cross-section was studied with the application of a gamma-ray densitometer. The study refers to the effect of mixture velocity, overall concentration, and angle of Pipe inclination on chord-averaged concentration profiles and local concentration maps, and flow behaviour of the coarse particle-water mixtures. The study revealed that the coarse particle-water mixtures in the inclined Pipe sections were significantly stratified, the solid particles moved principally close to the Pipe Invert, and for higher and moderate flow velocities particle saltation becomes the dominant mode of particle conveying
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Concentration distribution and slip velocity of coarse-particle-water mixture in horizontal and inclined Pipe sections
2017Co-Authors: Vlasák PavelAbstract:Narrow particle size distribution basalt pebbles of mean particle size 11.5 mm conveyed by water in the Pipe sections of different inclination were investigated on an experimental Pipe loop of inner diameter D = 100 mm. Mixture flow-behaviour and the concentration distribution were studied in a Pipe viewing section and with the application of a gamma-ray densitometer. The study refers to the effect of mixture velocity, overall concentration, and angle of Pipe inclination on chord-averaged concentration profiles and local concentration maps. The study revealed that the coarse particle-water mixtures in the inclined Pipe sections were significantly stratified, the solid particles moved principally close to the Pipe Invert, and for higher and moderate flow velocities particle saltation becomes the dominant mode of particle conveying
Reginold, Jesuthasan Terence - One of the best experts on this subject based on the ideXlab platform.
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Rocker Pipe solution to alleviate settlement induced distress in flexible Pipes
2006Co-Authors: Reginold, Jesuthasan TerenceAbstract:A number of earlier researchers investigated the soil structure interaction parameters which affect the structural behaviour of buried flexible Pipes. However, it was not until the mid-1990s that the importance of rocker Pipe design to accommodate differential settlement raised awareness of the consequent absence in current design procedure [BS EN 1295-3; 1998]. This study widens the understanding of the effect of differential ground movements on the behaviour of flexible Pipes to address concerns raised to the Committee European de Normalisation. Many Pipeline failures result from the excessive strains developed in the vicinity of the junction between a Pipe and a settling structure. Case studies of such failures are presented in this thesis, which demonstrates that it can occur not only in large diameter Pipeline but also in small diameter domestic Pipeline systems. A method of analysis and the use of developed appropriate rocker Pipe length is an industrially useful outcome of this research. Analytical solutions for flexible Pipes have been developed based on the concept of beams on elastic foundation approach. Non-dimensional relationships have been developed and are presented in the form of charts. These charts permit hand calculations and rapid verification of structural design of the Pipeline and, thus, assess the integrity of the existing Pipelines located in areas with ground instability. Knowledge of the soil strength and sub-grade modulus is required, along with Pipeline geometry and Pipe stiffness, to apply the non-dimensional relationships. The soil parameters can be measured in situ or estimated using empirical correlations. The cause for failure has been investigated with the proposed analytical soil structure interaction approach which identifies the zone of distress in the Pipeline. The analysis has been extended to demonstrate how a rocker Pipe system can be incorporated to alleviate such distress. The concept of rocker Pipes has also been investigated in the study through laboratory scale testing. Soil box tests, with ground conditions defined through plate/Pipe load testing, have been developed. Full-scale testing on flexible Pipes instrumented with FlexiForce pressure sensors at the Pipe Invert, strain gauges measuring strain due to induced differential settlement on the Pipe crown and deflection transducers measuring deflection profiles along the Pipe length due to differential settlement of the end structure, have been used to validate the mathematical modelling. Ile combination of rocker Pipes with flexible joints and elastic effects removes the distress imposed by the differential settlement, and provides the possibility for a better comparison with the data obtained from both theoretical analysis and experimental tests. Results from each of these approaches are compared with those from experiments. It is concluded that there is need for a rational design procedure analysis for rocker Pipes to be incorporated into codes of practice, such as EN 1295.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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Rocker Pipe solution to alleviate settlement induced distress in flexible Pipes
2006Co-Authors: Reginold, Jesuthasan TerenceAbstract:A number of earlier researchers investigated the soil structure interaction parameters which affect the structural behaviour of buried flexible Pipes. However, it was not until the mid-1990s that the importance of rocker Pipe design to accommodate differential settlement raised awareness of the consequent absence in current design procedure [BS EN 1295-3; 1998]. This study widens the understanding of the effect of differential ground movements on the behaviour of flexible Pipes to address concerns raised to the Committee European de Normalisation. Many Pipeline failures result from the excessive strains developed in the vicinity of the junction between a Pipe and a settling structure. Case studies of such failures are presented in this thesis, which demonstrates that it can occur not only in large diameter Pipeline but also in small diameter domestic Pipeline systems. A method of analysis and the use of developed appropriate rocker Pipe length is an industrially useful outcome of this research. Analytical solutions for flexible Pipes have been developed based on the concept of beams on elastic foundation approach. Non-dimensional relationships have been developed and are presented in the form of charts. These charts permit hand calculations and rapid verification of structural design of the Pipeline and, thus, assess the integrity of the existing Pipelines located in areas with ground instability. Knowledge of the soil strength and sub-grade modulus is required, along with Pipeline geometry and Pipe stiffness, to apply the non-dimensional relationships. The soil parameters can be measured in situ or estimated using empirical correlations. The cause for failure has been investigated with the proposed analytical soil structure interaction approach which identifies the zone of distress in the Pipeline. The analysis has been extended to demonstrate how a rocker Pipe system can be incorporated to alleviate such distress. The concept of rocker Pipes has also been investigated in the study through laboratory scale testing. Soil box tests, with ground conditions defined through plate/Pipe load testing, have been developed. Full-scale testing on flexible Pipes instrumented with FlexiForce pressure sensors at the Pipe Invert, strain gauges measuring strain due to induced differential settlement on the Pipe crown and deflection transducers measuring deflection profiles along the Pipe length due to differential settlement of the end structure, have been used to validate the mathematical modelling. Ile combination of rocker Pipes with flexible joints and elastic effects removes the distress imposed by the differential settlement, and provides the possibility for a better comparison with the data obtained from both theoretical analysis and experimental tests. Results from each of these approaches are compared with those from experiments. It is concluded that there is need for a rational design procedure analysis for rocker Pipes to be incorporated into codes of practice, such as EN 1295
Pavel Vlasak - One of the best experts on this subject based on the ideXlab platform.
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Effect of Pipe inclination on flow behaviour of fine-grained settling slurry
EPJ Web of Conferences, 2019Co-Authors: Pavel Vlasak, Zdenek Chara, Jiri Konfrst, Václav Matoušek, Mikoláš KeselyAbstract:The effect of flow parameters of fine-grained settling slurry on the pressure drop-velocity relationship, deposition limit velocity and local concentration distribution was studied in an experimental Pipe loop of inner diameter D = 100 mm with inclinable Pipe sections for Pipe inclination ranging from – 45° to +45° . The slurry consisted from water and narrow particle size distribution glass beads of mean diameter d50 = 0.18 mm. The concentration distribution was studied with application of a gamma-ray densitometry. The deposition velocity was defined as the flow velocity at which stationary deposit started to be formed at the Pipe Invert. The study revealed the stratified flow pattern of the studied slurry in inclined Pipe sections, for slurry velocities below to the deposition limit sliding or stationary bed were created in ascending Pipe sections. For low Pipe inclination (α ) the effect of inclination on local concentration distribution was not significant. Mean transport concentration for descending flow was lower than that for the ascending flow Deposition limit in inclined Pipe was slightly lower than that in horizontal Pipe. Frictional pressure drops in ascending Pipe were higher than that in descending Pipe, the difference decreased with increasing velocity and inclination.
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Coarse particles-water mixtures flow in Pipes
2017Co-Authors: Pavel VlasakAbstract:The present paper is focused on evaluation of the effect of average mixture velocity and overall concentration on the pressure drop versus the slurry average velocity relationship, on slurry flow behaviour and local concentration distribution. The experimental investigation was carried out on the Pipe loop of inner diameter D =100 mm, which consists of smooth stainless steel Pipes and horizontal, inclinable and vertical Pipe sections. The frictional pressure drop in the horizontal Pipe section were significantly higher than that in the vertical Pipe due to the fact, that for stratified flow the contact load produced significant energy losses. The frictional pressure drop of coarse particles mixtures in vertical Pipe increased with the increasing mixture concentration and velocity, what confirmed effect of inner friction, inter-particles collision, and the drag due to particle-liquid slip. It was found that for stratified coarse particles-water mixture the frictional pressure drop was not significantly influenced by the Pipe inclination, especially for low concentration values. The effect of Pipe inclination decreased with increasing mixture velocity in ascending Pipe section; the maximum value was reached for inclination between 20 and 40 degrees. Inclination of pressure drop maximum increased with decreasing mixture velocity. In descending Pipe section the frictional pressure drop gradually decreased with increasing Pipe inclination. The effect of inclination on frictional pressure drops could be practically neglected, especially for low mixture concentration and higher flow velocities. The study revealed that the coarse particle-water mixtures in the horizontal and inclined Pipe sections were significantly stratified. The particles moved principally in a layer close to the Pipe Invert. However, for higher and moderate flow velocities the particles moved also in the central part of the Pipe cross-section, and particle saltation [1] was found to be dominant mode of particle conveying.
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Experimental investigation of coarse particle conveying in Pipes
'EDP Sciences', 2015Co-Authors: Pavel Vlasak, Zdenek Chara, Jiri Konfrst, Jan KrupičkaAbstract:The advanced knowledge of particle-water mixture flow behaviour is important for safe, reliable, and economical design and operation of the freight Pipelines. The effect of the mixture velocity and concentration on the coarse particle – water mixtures flow behaviour was experimentally investigated on an experimental Pipe loop of inner diameter D = 100 mm with horizontal, vertical, and inclined Pipe sections. Narrow particle size distribution basalt pebbles were used as model of coarse-grained solid particles. The radiometric method was used to measure particle concentration distribution in Pipe cross-section. Mixture flow behaviour and particles motion along the Pipe Invert were studied in a Pipe viewing section. The study revealed that the coarse particlewater mixtures in the horizontal and inclined Pipe sections were significantly stratified. The particles moved principally in a layer close to the Pipe Invert. However, for higher and moderate flow velocities the particles moved also in the central part of the Pipe cross-section, and particle saltation was found to be dominant mode of particle conveying
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flow structure of coarse grained slurry in a horizontal Pipe
Journal of Hydrology and Hydromechanics, 2012Co-Authors: Pavel Vlasak, Bohus Kysela, Zdenek CharaAbstract:The flow behaviour of coarse-grained slurry depends on particle size, shape, density and concentration, and on the density and rheological properties of the carrier liquid. The present paper describes the results of an experimental investigation and flow visualisation of model coarse-grained particle-water mixtures in a closed Pipe loop with smooth stainless steel Pipes of inner diameter 36 mm. Glass balls and washed graded pebble gravel of mean diameter d50 = 6 mm were used as model coarse-grained material. The effect of slurry velocity and particle concentration on the slurry flow behaviour and pressure drop in the turbulent regime was evaluated. Particle distribution in the Pipe cross-section and motion of particles along the Pipe Invert, particle saltation and particle conveying in the carrier liquid were investigated in a transparent Pipe viewing section and motion of individual particles was described. Velocity profiles of the carrier liquid and conveyed particles were determined.
Sheehan Therese - One of the best experts on this subject based on the ideXlab platform.
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Protection of buried rigid Pipes using geogrid-reinforced soil systems subjected to cyclic loading
'Elsevier BV', 2021Co-Authors: Elshesheny Ahmed, Mohamed, Mostafa H.a., Sheehan ThereseAbstract:YesThe performance of buried rigid Pipes underneath geogrid-reinforced soil while applying incrementally increased cyclic loading was assessed using a fully instrumented laboratory rig. The influence of varying two parameters of practical importance was investigated; the Pipe burial depth and the number of geogrid-layers. Measurements were taken for Pipe deformation, footing settlement, strain in Pipe and reinforcing layers, and pressure/soil stress on the Pipe crown during various stages of cyclic loading. The research outcomes demonstrated a rapid increase in the rate of deformation of the Pipe and the footing, and the rate of generated strain in the Pipe and the geogrid-layers during the first 300 cycles. While applying further cycles, those rates were significantly decreased. Increasing the Pipe burial depth and number of geogrid-layers resulted in reductions in the footing and the Pipe deformations, the pressure on Pipe crown, and the Pipe strains. Redistribution of stresses, due to the inclusion of reinforcing layers, formed a confined zone surrounding the Pipe providing it with additional lateral support. The Pipe Invert experienced a rebound, which was found to be dependent on pressure around the Pipe and the degree of densification of the bedding layer. Data for strains measured in the geogrid-layers showed that despite the applied loading value and the Pipe burial depth, the tensile strain in the lower geogrid-layer was usually higher than that measured in the upper layer
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Protection of buried rigid Pipes using geogrid-reinforced soil systems subjected to cyclic loading
'Elsevier BV', 2021Co-Authors: Elshesheny Ahmed, Mohamed, Mostafa H.a., Sheehan ThereseAbstract:YesThe performance of buried rigid Pipes underneath geogrid-reinforced soil while applying incrementally increased cyclic loading was assessed using a fully instrumented laboratory rig. The influence of varying two parameters of practical importance was investigated; the Pipe burial depth and the number of geogrid-layers. Measurements were taken for Pipe deformation, footing settlement, strain in Pipe and reinforcing layers, and pressure/soil stress on the Pipe crown during various stages of cyclic loading. The research outcomes demonstrated a rapid increase in the rate of deformation of the Pipe and the footing, and the rate of generated strain in the Pipe and the geogrid-layers during the first 300 cycles. While applying further cycles, those rates were significantly decreased. Increasing the Pipe burial depth and number of geogrid-layers resulted in reductions in the footing and the Pipe deformations, the pressure on Pipe crown, and the Pipe strains. Redistribution of stresses, due to the inclusion of reinforcing layers, formed a confined zone surrounding the Pipe providing it with additional lateral support. The Pipe Invert experienced a rebound, which was found to be dependent on pressure around the Pipe and the degree of densification of the bedding layer. Data for strains measured in the geogrid-layers showed that despite the applied loading value and the Pipe burial depth, the tensile strain in the lower geogrid-layer was usually higher than that measured in the upper layer.The full-text of this article will be released for public view at the end of the publisher embargo on 5 Jun 2021
Byrne B - One of the best experts on this subject based on the ideXlab platform.
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Sequential limit analysis of Pipe-soil interaction during large-amplitude cyclic lateral displacements
'University Service Publishing', 2017Co-Authors: Kong D, C.m. Martin, Byrne BAbstract:A newly developed sequential limit analysis (SLA) technique is used to perform large-displacement numerical simulations relevant to thermally-induced lateral buckling of untrenched subsea Pipelines. A rigid plane-strain Pipe segment, partially embedded in undrained clay, is subjected to cyclic lateral displacements with amplitudes of up to eight Pipe diameters. A constant vertical dead load is applied to the Pipe during each lateral sweep, but in some analyses this load is varied from one sweep to the next. The SLA method directly models the evolution of the soil surface profile, including active and dormant berms, and incorporates strain softening behaviour caused by soil remoulding. Comparisons of the numerical results with published centrifuge model test data, for a range of loading cases, are provided in terms of the Pipe Invert trajectory and lateral soil resistance. There is good overall agreement between the numerical and experimental results, demonstrating the suitability of SLA for solving such problems. Detailed aspects of the cyclic loading behaviour are discussed with reference to soil failure mechanisms and bearing capacity failure envelopes for combined vertical and horizontal loading. Finally, two brief parametric studies are used to explore the effects of the initial Pipe embedment and vertical loading history on the subsequent lateral loading behaviour